PROJECT SUMMARY The long-term goal of this research is to develop technologies that facilitate motor learning after stroke. Motor learning is an essential component of stroke rehabilitation, as stroke-survivors must adapt to a changed nervous system to generate desired movements. While much emphasis has been placed on teaching volitional actions to stroke survivors, unimpaired motor control relies heavily on involuntary sensorimotor feedback pathways that can influence motor outputs as required to adapt to novel tasks or environments. In particular, feedback pathways that generate rapid motor responses to proprioceptive or visual inputs play crucial role in motor learning by guiding corrective motor responses. Rapid motor corrections by proprioceptive and visual pathways can serve as a potentially powerful tool to guide motor rehabilitation after stroke, but first, a more complete assessment of post-stroke deficits in these pathways ? specifically their impacts on motor learning ? is required. Therefore, this proposal will focus on quantifying post-stroke impairments in proprioceptive and visual pathways that contribute to rapid motor responses, and determining how such impairments affect motor learning in this population. Specifically, Aim 1 will investigate how stroke alters the relative contributions of proprioceptive and visual pathways to rapid motor responses. A virtual reality and robotic system will be used to perturb sensory information during reaching to quantitatively assess the degree to which proprioceptive and visual contributions to rapid motor responses remain independent after stroke. Aim 2 will investigate how the integrity of proprioceptive and visual contributions to rapid motor responses affects motor learning after stroke. A virtual reality and robotic system will be used to create training environments that amplify the proprioceptive or visual consequences of reaching errors. Using these training environments, I will examine whether the ability to adapt rapid motor responses is impaired after stroke, and how such impairment influences motor learning. Subjects with a range of impairment levels, assessed by traditional clinical scales, will be included in this study to determine how rapid, corrective motor behaviors and learning are affected by stroke severity. The proposed study will elucidate the role of involuntary sensorimotor feedback pathways during motor learning following stroke, and provide a means to quantify subject-specific impairments in these pathways. Together, the results from the proposed study will inform the development of patient-specific treatments for this population.